For example, US 2006/0222538 A1 (JP-A-2006-307829)) discloses a high-pressure fuel pump, which has a passage for returning fuel from an accumulation chamber into a compression chamber of the high-pressure fuel pump by bypassing a discharge valve when the high-pressure fuel pump is being stopped.
In the high-pressure fuel pump of US 2006/0222538 A1, the high-pressure fuel pump includes a functional component such as a discharge valve and has a mounting hole, which is provided in a housing for mounting the functional component. In the present structure, the functional component and the mounting hole therebetween define a clearance as a passage, through which fuel is returned from the accumulation chamber into the compression chamber. In the present structure, when the high-pressure fuel pump is being stopped, fuel at high pressure in the accumulation chamber is returned into the compression chamber so as to reduce fuel pressure in the accumulation chamber. Whereby, the fuel, which is discharged during pump operation, is restricted from returning into the compression chamber through the passage, and thus the volume efficiency of the pump is maintained.
For example, JP-A-4-86370 discloses a high-pressure fuel pump including a discharge valve having a valve element, which has a passage communicating the upstream of the valve element with the downstream of the valve element. The passage accommodates another valve element, which allows only flow of fuel from the downstream to the upstream, and a biasing unit that biases the other valve element in a valve closing direction. In the present structure, fuel pressure at the downstream side with respect to the discharge valve is maintained at a predetermined pressure after the high-pressure fuel pump is stopped.
In the high-pressure fuel pump disclosed in US 2006/0222538 A1, the passage is formed by the clearance between the components, and the passage is configured to restrict the flow rate of fuel passing therethrough. However, in the structure of US 2006/0222538 A1, the passage is regularly opened. Accordingly, fuel pressure in the accumulation chamber decreases to comparatively low pressure in the compression chamber, after the pump is stopped.
The inventor conceived to combine the valve element and the biasing unit disclosed in JP-A-4-86370 with the passage disclosed in US 2006/0222538 A1 so as to maintain the predetermined fuel pressure without decreasing fuel pressure in the accumulation chamber to fuel pressure in the compression chamber. However, the structure may be complicated by simply providing the valve element and the biasing unit disclosed in JP-A-4-86370 in the passage disclosed in US 2006/0222538 A1.